A far ultraviolet photoelectron spectrometer equipped with the open counter was prepared, which can detect, in open-air, outer-orbital electrons excited by photons with energies up to 7.0 eV. Several OLED materials were employed to confirm performance of the spectrometer. The ionization potential of Hexaphenylcyclotrisiloxane (DPSiO3) is estimated to be 6.49eV. The near edge structure of poly (9,9-dioctylfluorence) (F8) was investigated by the spectrometer successfully.